Effects of neighbourhood structure and tussock dynamics on genet demography of Festuca rubra in a mountain meadow

1. We examined whether genet demography in the clonal grass Festuca rubra in a mountain grassland in the Krkonose Mountains (Czech Republic) changes in response to local environment. The data were also used to compare genet recruitment with estimates of genet mortality. 2. We sampled F. rubra from four permanent plots in which ramet densities of all species have been recorded at a fine scale for a decade. Identities of 224 ramets were assessed by means of RAPD, yielding 145 different genets, of which most (68%) were found only once. The genet with the highest number of sampled ramets was recorded nine times. 3. By assuming that the probability that two ramets are genetically identical is a function of distance between ramets, we estimated that successful seedling recruitment rates were between 0.15 and 16 genets m(-2) yr(-1) depending on the plot. Genet mortality was estimated from ramet mortality using the assumption that ramet mortality was uncorrelated over space. In three of the four plots, genet mortalities fell into the same range as the genet recruitment rates. 4. The total number of genets per unit area must be known to enable determination of per capita recruitment and mortality rates. We developed an estimation technique involving simulation of the sampling process, which yielded values of 231-968 genets m(-2). Genet turnover was therefore low (0.1-1% annually) and the high genet diversity is maintained by a very low recruitment. 5. Spatial analysis showed that two ramets were more likely to be genetically identical when they came from a microhabitat where Festuca ramet density had recently increased; patches in which Festuca ramet density had decreased were more likely to contain ramets from several genets. Expanding tussocks are thus more likely to be composed of ramets of one genet only. Density and biomass of other species in the neighbourhood showed little correlation with the genet structure of Festuca rubra. 6. Although ramets of Festuca rubra intermingle with other species at a fine scale, the population biology of its genets is driven mainly by the dynamics of its own ramets. Interactions with other species and response to local environments have little effect on genet structure.